Effect Measure

DDT has a checkered history, to be sure. Many of us remember walking through clouds of it in our childhoods, as it was sprayed willy-nilly for nuisance mosquitoes. The discovery that it was persistent in the environment (didn’t break down) and harmed birds by thinning their egg shells (Rachel Carson’s “silent spring”) eventually led to its withdrawal from use. It is banned in the US, although it is not banned worldwide and is still used for vital public health purposes. Most of the actual uses during its heyday were for economic or aesthetic purposes with no public health rationale. Its disappearance for these uses has been a good thing. Through all the controversy (most of it stimulated by agribusiness who liked DDT’s effectiveness and cheapness), there has been uncertainty about its effect on people. In the last few years various epidemiological studies of breast cancer failed to find a connection with that dread disease. Now a new study does find one and suggests why the others haven’t. In breast cancer, as in the rest of life, timing is everything:

Women heavily exposed to the pesticide DDT during childhood are five times as likely to develop breast cancer, a new scientific study suggests.

For decades, scientists have tried to determine whether there is a connection between breast cancer and DDT, the most widely used insecticide in history. The UC Berkeley research, based on a small number of Bay Area women, tested a theory that the person’s age during exposure was critical, and provided the first evidence of a substantial effect on breast cancer.

“There was very broad exposure to this pesticide, and with this study, we have evidence that women exposed when young were the most affected,” said Barbara A. Cohn, director of UC Berkeley’s Child Health and Development Studies, who led the study of 129 women. “If this finding holds up, those who were young and more highly exposed could be the women at greatest risk.”

Women born between 1945 and 1965 were most likely to have been heavily exposed as children to DDT, which was sprayed throughout the United States to kill mosquitoes and other insects. DDT use began in 1945, peaked in 1959 and was banned nationwide in 1972 because it was building up in the environment. (LA Times)

The unique feature of this study is the availability of stored serum samples from women who gave birth to children in the 1959 – 1967 period, a time when DDT was still used in high volume and before any of them developed breast cancer. In considering the group who developed breast cancer later (median time to diagnosis was 17 years post sample), those with the highest DDT levels and who were born after 1931 had a five fold elevated breast cancer risk. The 1931 date was chosen because those women would have been 14 years old or less in 1945 when DDT use started in earnest in the US. The data thus suggest that it is the timing of exposure which is critical, not just some later measured value of DDT metabolites in middle aged women, the usual subjects of the DDT breast cancer studies. Early exposures (adolescence and childhood) are the key to DDT risk in these data.

This is one study, albeit a well conducted one by experienced investigators. It is also relatively small, limited by the number of historical stored serum samples. But the effect is large, which makes it less likely we are seeing the consequences of some hidden bias (an unmeasured variable related to breast cancer risk that differs dramatically in the high DDT group versus its comparison). It is possible for such differences to exist, but for such a large effect the unmeasured variable (an uncontrolled confounder) would have to be a powerful risk factor we don’t know about. Possible. Not that likely.

Confirmation and further work are needed — as always: when have scientists not asked for it? But these data are concrete evidence that the caution about human exposure to DDT was warranted and banning its use in the US was of benefit to more than birds.


  1. #1 Keith O'Connor
    October 2, 2007

    I remember when I was a kid, maybe in about 1954, we all used to run right behind the “bug truck” and breathe in the fumes. We thought it was the best fun. We did it every time the truck drove by. All the kids did.


  2. #2 glock
    October 2, 2007

    OMG…! We used to ride our bikes behind the trucks. I thought we were the only ones. It seemed like a fun idea at the time……. That ugly little memory pops into my head every time the the term DDT comes up. I can still remember the smell.

    Is DDT and /or it’s metabolites still measurable 40 to 50+ years later with regard to being able to ascertain ones level of past exposure???

  3. #3 M. Randolph Kruger
    October 3, 2007

    Revere-I thought it was the breakdown of DDT that caused breast cancer…. Something like DDE or DDC. Cant remember. It was the 60’s.

  4. #4 revere
    October 3, 2007

    Randy: Not the issue, here. The metabolites of DDT are used as a measure of exposure. If DDT exposure causes breast cancer we still need to know the mechanism, which may or may not involve a metabolite.

  5. #5 Ed Darrell
    October 3, 2007

    Considering the way the metabolites of DDT mimic estrogen, isn’t estrogen poisoning a solid candidate for the culprit in the breast cancers?

  6. #6 ben
    October 4, 2007

    I’m a little curious how women living in the same general area at the same time have such different exposure levels to DDT. This leads me to wonder if there was something else about where and how they lived that would not only increase their exposure to DDT, but to some other factor that could be related to increase in risk of developing breast cancer.

  7. #7 revere
    October 4, 2007

    ben: It’s not that hard to figure. DDT spraying could be very local, as those of us who walked through clouds of it will testify.

  8. #8 ben
    October 4, 2007

    Yes, I’m sure that’s true. That is all well before my time, thankfully.

  9. #9 Hans Erren
    October 7, 2007

    Radioactive Fallout anybody? Between 1945 and 1974 also atmospheric nuclear tests were held.

  10. #10 kyangadac
    October 12, 2007

    Radioactivity doesn’t work Hans because breast cancer has some other epidemiological variations, namely, it’s higher in women who haven’t breast fed and in women who are overweight – or have a high fat intake (amongst others). Both these variables point to a fat soluble cause. Also, it’s worth pointing out that if DDT is associated with breast cancer then similar chemicals such as dieldrin, heptachlor and PCB’s may also be associated with breast cancer.
    One of the problems with many studies done in the past is that it is easy to get a null(no association) result if you don’t control for these and other confounding factors. One important thing about this study is that it used really early serum samples(pre-1970) when these confounding chemicals were not so widespread.
    A search of the back issues of Rachel’s Weekly for ‘breast cancer’ will provide you with more than enough evidence of why this link is (a)likely to be true and (b)has been suppressed for so long.

  11. #11 M. Randolph Kruger
    March 5, 2008

    Knock me over with a feather please……..


    Comments Revere? I was stunned, absolutely so….

  12. #12 revere
    March 5, 2008

    Randy; This business of a supposed WHO DDT ban is utter nonsense. Tim Lambert at Deltoid has covered this repeatedly: http://scienceblogs.com/deltoid/2006/09/politically_based_medicine_at.php

    DDT is pesticide of choice in certain circumstances because of the residual. The problem in the US was that it was used wholesale by agribusiness, not for malaria. This is old news.

  13. #13 Hank Roberts
    April 1, 2008

    Tangentially related:

    Association between prenatal pesticide exposures and the generation of leukemia-associated T(8;21).
    Pediatr Blood Cancer. 2007 Oct 15;49(5):624-8.
    BACKGROUND: This study was designed to investigate the relationship between prenatal pesticide exposures and the generation of leukemia-associated t(8;21)(q22;q22), one of the most common cytogenetic abnormalities in childhood acute myeloid leukemia (AML). ….
    CONCLUSION: These results further confirm the prenatal origin of t(8;21) and establish a significant correlation between prenatal pesticide exposures and the generation of t(8;21). They suggest that prenatal pesticide exposures may be causal factors for the generation of leukemia-associated chromosomal translocations.

  14. #14 Dr. Mary Rose Paster
    November 15, 2009

    Just discovered that 7 of us that lived on ex-farms in the 1950’s, likely loaded with DDT, all developed rare and invasive fibroid tumors in our early 20’s with full hysterectomies in our 20’s. Anyone out there hear anything similar or aware of any research regarding impact of xenoestrogene (DDT) exposure in childhood and development of early gynecological pathology? So far we are 7 out of about 50 girls. There may be others.

  15. #15 Diana G. Baker
    Kenner, Louisiana 1949 through 1961 -
    February 8, 2013

    Dr. Mary Rose Paster I also had those issues in my early 20’s with hysterectomy and fibroid tumors. Now at 63 I have breast cancer HERS.

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